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Get rid of large stack buffers in PSA sign wrapper

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Manuel Pégourié-Gonnard 2018-11-13 10:32:00 +01:00 committed by Hanno Becker
parent fe8607350c
commit f127e6080e
1 changed files with 101 additions and 79 deletions
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180
library/pk_wrap.c
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@ -761,88 +761,13 @@ static int pk_opaque_can_do( mbedtls_pk_type_t type )
type == MBEDTLS_PK_ECDSA );
}
/* Like mbedtls_asn1_write_mpi, but from a buffer */
static int asn1_write_mpibuf( unsigned char **p, unsigned char *start,
const unsigned char *src, size_t slen )
/* translate PSA errors to best PK approximation */
static int pk_err_from_psa( psa_status_t status )
{
int ret;
size_t len = 0;
if( (size_t)( *p - start ) < slen )
return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
len = slen;
*p -= len;
memcpy( *p, src, len );
if( **p & 0x80 )
{
if( *p - start < 1 )
return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
*--(*p) = 0x00;
len += 1;
}
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_INTEGER ) );
return( (int) len );
}
/* Transcode signature from PSA format to ASN.1 sequence.
* See ecdsa_signature_to_asn1 in ecdsa.c.
*
* [in] sig: the signature in PSA format
* [in/out] sig_len: signature length pre- and post-transcoding
* [out] dst: the signature in ASN.1 format
*/
static int pk_ecdsa_sig_asn1_from_psa( const unsigned char *sig, size_t *sig_len,
unsigned char *dst )
{
int ret;
unsigned char buf[MBEDTLS_ECDSA_MAX_LEN];
unsigned char *p = buf + sizeof( buf );
size_t len = 0;
const size_t mpi_len = *sig_len / 2;
MBEDTLS_ASN1_CHK_ADD( len, asn1_write_mpibuf( &p, buf, sig + mpi_len, mpi_len ) );
MBEDTLS_ASN1_CHK_ADD( len, asn1_write_mpibuf( &p, buf, sig, mpi_len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &p, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &p, buf,
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
memcpy( dst, p, len );
*sig_len = len;
return( 0 );
}
static int pk_opaque_sign_wrap( void *ctx, mbedtls_md_type_t md_alg,
const unsigned char *hash, size_t hash_len,
unsigned char *sig, size_t *sig_len,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
{
const psa_key_slot_t *key = (const psa_key_slot_t *) ctx;
psa_status_t status;
psa_algorithm_t alg = PSA_ALG_ECDSA( mbedtls_psa_translate_md( md_alg ) );
/* PSA needs a buffer of know size */
unsigned char buf[2 * MBEDTLS_ECP_MAX_BYTES];
const size_t buf_len = sizeof( buf );
/* PSA has its own RNG */
(void) f_rng;
(void) p_rng;
status = psa_asymmetric_sign( *key, alg, hash, hash_len,
buf, buf_len, sig_len );
/* translate errors to best approximation */
switch( status )
{
case PSA_SUCCESS:
break; /* don't return now */
return( 0 );
case PSA_ERROR_NOT_SUPPORTED:
return( MBEDTLS_ERR_PK_FEATURE_UNAVAILABLE );
case PSA_ERROR_INSUFFICIENT_MEMORY:
@ -858,12 +783,109 @@ static int pk_opaque_sign_wrap( void *ctx, mbedtls_md_type_t md_alg,
default: /* should never happen */
return( MBEDTLS_ERR_PK_HW_ACCEL_FAILED );
}
}
pk_ecdsa_sig_asn1_from_psa( buf, sig_len, sig );
/*
* Like mbedtls_asn1_write_mpi(), but from a buffer.
*
* p: pointer to the end of the output buffer
* start: start of the output buffer, and also of the mpi to write at the end
* n_len: length ot the mpi to read from start
*/
static int asn1_write_mpibuf( unsigned char **p, unsigned char *start,
size_t n_len )
{
int ret;
size_t len = 0;
if( (size_t)( *p - start ) < n_len )
return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
len = n_len;
*p -= len;
memmove( *p, start, len );
/* if the msb is 1, ASN.1 requires that we prepend a 0.
* we're never called with n_len == 0, so we can always read back a byte */
if( **p & 0x80 )
{
if( *p - start < 1 )
return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
*--(*p) = 0x00;
len += 1;
}
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start,
MBEDTLS_ASN1_INTEGER ) );
return( (int) len );
}
/* Transcode signature from PSA format to ASN.1 sequence.
* See ecdsa_signature_to_asn1 in ecdsa.c, but with byte buffers instead of
* MPIs, and in-place.
*
* [in/out] sig: the signature pre- and post-transcoding
* [in/out] sig_len: signature length pre- and post-transcoding
* [int] buf_len: the available size the in/out buffer
*/
static int pk_ecdsa_sig_asn1_from_psa( unsigned char *sig, size_t *sig_len,
size_t buf_len )
{
int ret;
size_t len = 0;
const size_t rs_len = *sig_len / 2;
unsigned char *p = sig + buf_len;
MBEDTLS_ASN1_CHK_ADD( len, asn1_write_mpibuf( &p, sig + rs_len, rs_len ) );
MBEDTLS_ASN1_CHK_ADD( len, asn1_write_mpibuf( &p, sig, rs_len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &p, sig, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &p, sig,
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
memmove( sig, p, len );
*sig_len = len;
return( 0 );
}
static int pk_opaque_sign_wrap( void *ctx, mbedtls_md_type_t md_alg,
const unsigned char *hash, size_t hash_len,
unsigned char *sig, size_t *sig_len,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
{
const psa_key_slot_t *key = (const psa_key_slot_t *) ctx;
psa_algorithm_t alg = PSA_ALG_ECDSA( mbedtls_psa_translate_md( md_alg ) );
size_t bits, buf_len;
psa_status_t status;
/* PSA has its own RNG */
(void) f_rng;
(void) p_rng;
/* PSA needs an output buffer of known size, but our API doesn't provide
* that information. Assume that the buffer is large enough for a
* maximal-length signature with that key (otherwise the application is
* buggy anyway). */
status = psa_get_key_information( *key, NULL, &bits );
if( status != PSA_SUCCESS )
return( pk_err_from_psa( status ) );
buf_len = MBEDTLS_ECDSA_MAX_SIG_LEN( bits );
/* make the signature */
status = psa_asymmetric_sign( *key, alg, hash, hash_len,
sig, buf_len, sig_len );
if( status != PSA_SUCCESS )
return( pk_err_from_psa( status ) );
/* transcode it to ASN.1 sequence */
return( pk_ecdsa_sig_asn1_from_psa( sig, sig_len, buf_len ) );
}
const mbedtls_pk_info_t mbedtls_pk_opaque_info = {
MBEDTLS_PK_OPAQUE,
"Opaque",